1. Field of the Invention
The present invention generally relates to a method for fabricating devices on semiconductor substrates. More specifically, the present invention relates to a method of etching magnetic materials.
2. Description of the Related Art
Microelectronic devices are generally fabricated on a semiconductor substrate as integrated circuits wherein various conductive layers are interconnected to one another to facilitate propagation of electronic signals within the device. An example of such a device is a storage element in memories such as magneto-resistive random access memories (MRAM) that facilitate storage of digital information.
A memory cell in a MRAM device is a multi-layered structure comprising two sets of magnetic layers that are separated by a non-magnetic dielectric material. These layers are deposited as overlying blanket films, and then patterned to form the MRAM device. More specifically, the MRAM device comprises a top electrode (e.g., tantalum (Ta), tantalum nitride (TaN), and the like), a free magnetic layer (e.g., NiFe, CoFe, and the like), a tunnel layer (e.g., Al2O3 and the like), a multi-layer magnetic stack comprising layers of NiFe, ruthenium (Ru), CoFe, PtMn, NiFeCr, and the like, a bottom electrode (e.g., Ta, TaN, and the like), and a barrier layer (e.g., SiO2 and the like).
Fabrication of a MRAM device comprises plasma etching processes in which one or more layers of a MRAM film stack are removed, either partially or in total. The MRAM film stack comprises materials that are sensitive to corrosion and may be easily oxidized, eroded, or damaged during etching, as well as develop difficult to remove metal-containing residues. These problems arise from low etch selectivity and non-volatile nature of by-products that form during the etch processes. Such residues generally build up along the sides of the MRAM film stack and may form a veil-like pattern. The conductive residues or eroded layers may cause electrical short-circuits within the MRAM film stack.
The magnetic materials are generally etched using a chlorine (Cl) based chemistry that has low etch selectivity for the magnetic material (e.g., NiFe, CoFe, and the like) over the material of the tunnel layer (e.g., Al2O3 and the like) and photoresist. As a result of this low etch selectivity, the etch processes require use of a hard mask and may simultaneously etch both the top magnetic layer and tunnel layer, thereby exposing the sidewalls of the tunnel layer to plasma erosion and deposition of conductive residues. Application and removal of the hard etch mask are time consuming routines that decrease productivity and increase the costs of fabricating the MRAM devices. Additionally, the eroded tunnel layer or conductive residues may cause electrical short-circuits within the MRAM device (e.g., between the magnetic layers separated by the tunnel layer), or may cause the MRAM device to operate sub-optimally or not at all.
Therefore, there is a need in the art for an improved method of etching magnetic materials for fabrication of a magneto-resistive random access memory (MRAM) device.